Power at Immersion Lenses

[Claire Brown]

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Hello All,

We are trying to measure the power of a light source through a 63x oil immersion lens. With the short focal distance the power we measure is highly dependent on the position of the sensor relative to the lens.

Can the power be measured this way or do we need to get a sensor that we can put oil on and use oil immersion to really get a proper measure of the power at the sample?


Sincerely,

Claire

[mmodel]

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Dear Clair,

I think there will be a lot of light loss due to total internal reflection if you don't use oil

Mike

________________________________
From: Confocal Microscopy List <[hidden email]> on behalf of Claire Brown, Dr. <[hidden email]>
Sent: Friday, March 15, 2019 11:08 AM
To: [hidden email]
Subject: Power at Immersion Lenses

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Hello All,

We are trying to measure the power of a light source through a 63x oil immersion lens. With the short focal distance the power we measure is highly dependent on the position of the sensor relative to the lens.

Can the power be measured this way or do we need to get a sensor that we can put oil on and use oil immersion to really get a proper measure of the power at the sample?


Sincerely,

Claire

[James Jonkman-2]

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Hi, Claire.  I can think of 2 ways to do this.  You could measure the power with a 10x objective, and then compare the transmission curves from the manufacturer for the 10x and the 63 objectives and estimate the correction.  The transmission of the objective would be the main difference, but depending on how the back aperture of the objective is filled this isn't perfect.  Second way would be to get a Thorlabs power meter - they have a microscope slide shaped sensor which is designed to accommodate immersion media (model S170C).  I use it with the PM400 touch screen - it's an excellent combination and worth the investment.  I also use it to log power fluctuations - you can set the data logging as fast as every 10 ms to watch for faster fluctuations, or for longer durations I set it to measure every 60s and walk away for a couple of hours.

(no commercial interest)

Cheers,
James

-----------------------------------------------
   James Jonkman, Manager
   Advanced Optical Microscopy Facility (AOMF)
   University Health Network
   MaRS, PMCRT tower, 101 College St., Room 15-305
   Toronto, ON, CANADA    M5G 1L7
   [hidden email]  Tel: [phone]  
   www.aomf.ca

[Jim Haley]

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Are you trying to measure relative light output at the various
proximities or absolute light output in terms of units such as Lux?

Thanks And Have a Great Day!

Jim Haley

 

******************************

Jim Haley

Applications Engineer

MVIA, Inc.

P.O. Box 161

Monaca, PA 15061

  voice:     [phone]

  fax:       [phone]

  e-mail:    [hidden email]  <mailto:[hidden email]>

  MVIA Website  <http://www.mvia.com/>

  Digital Microscope Cameras from MVIA  <http://www.mvia.com/Digcams/dig_cameras.html>

  Image Analysis Software from MVIA  <http://www.mvia.com/IASoftware/ia_software.html>  

******************************


On 3/15/2019 11:08 AM, Claire Brown, Dr. wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hello All,
>
> We are trying to measure the power of a light source through a 63x oil immersion lens. With the short focal distance the power we measure is highly dependent on the position of the sensor relative to the lens.
>
> Can the power be measured this way or do we need to get a sensor that we can put oil on and use oil immersion to really get a proper measure of the power at the sample?
>
>
> Sincerely,
>
> Claire
>

[Craig Brideau]

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As James mentioned, the S170C is designed for high NA oil and water
dipping/immersion lenses. Full disclosure Pina Colarusso and I helped Thor
with the prototype. If you use that one, the PM100D power meter is cheaper
than the PM400 and has similar logging features. Finally, don't directly
focus on the surface of the sensor, back away as much as practical without
causing the immersion medium to fall off the lens or 'funnel' too tightly.
You will get more accurate readings this way as you will be using more area
of the sensor and it tends to smooth out the reading.

Craig

On Fri, Mar 15, 2019 at 10:38 AM James Jonkman <[hidden email]>
wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi, Claire.  I can think of 2 ways to do this.  You could measure the
> power with a 10x objective, and then compare the transmission curves from
> the manufacturer for the 10x and the 63 objectives and estimate the
> correction.  The transmission of the objective would be the main
> difference, but depending on how the back aperture of the objective is
> filled this isn't perfect.  Second way would be to get a Thorlabs power
> meter - they have a microscope slide shaped sensor which is designed to
> accommodate immersion media (model S170C).  I use it with the PM400 touch
> screen - it's an excellent combination and worth the investment.  I also
> use it to log power fluctuations - you can set the data logging as fast as
> every 10 ms to watch for faster fluctuations, or for longer durations I set
> it to measure every 60s and walk away for a couple of hours.
>
> (no commercial interest)
>
> Cheers,
> James
>
> -----------------------------------------------
>    James Jonkman, Manager
>    Advanced Optical Microscopy Facility (AOMF)
>    University Health Network
>    MaRS, PMCRT tower, 101 College St., Room 15-305
>    Toronto, ON, CANADA    M5G 1L7
>    [hidden email]  Tel: [phone]
>    www.aomf.ca
>

[Benjamin Smith]

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*****

A few quick notes:
1) Be careful comparing between objectives.  Not only is the transmission
efficiency different, but the area of the back aperture is also different,
meaning the amount of light going into an objective also varies.  Also,
unless the light intensity profile at the back aperture is a perfectly
uniform top hat, the difference in light going into an objective won't be
as simple as the ratio of the back aperture areas.

2) With high NA objectives, you run into an additional problem of
increasing amounts of light reflecting off of the power meter (think
Brewster's angle).  As such, a lot of the marginal photons will reflect,
reducing the overall measurement.

3) As already mentioned, the back reflection due to the glass-air interface
at the objective lens will also reduce the amount of transmitted light
compared to a glass-oil interface, and even more so if the objective lens
is scratched or dirty.

4) Power meters can saturate and become non-linear if all the light is
shined on it in a very small area.  Ideally, you will want to cover as much
of the sensor as possible, especially at higher intensities.

With this in mind, a quick and dirty solution would be to get the objective
as close to (if not lightly touching) the sensor area as possible, and then
gradually increase the light intensity until you get a stable measurement.
Then gradually pull the objective away until you reach a peak power
reading.  The objective may need to be able to get within a millimeter of
the sensor to have the marginal rays stay within the sensor area.  Due to
the issues stated above, this will be a slight underestimation, but it will
definitely get you in the ball park.

If you need a much more accurate measurement, an oil immersion compatible
power meter seems the best (although fairly expensive) option:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=2191

One other option that comes to mind would be if you had an oil immersion
condenser, you could use it to recollimate the light from the first
objective, and then place the power meter at the back aperture of the
condenser.  With everything lined up correctly, and without any scattering
material between the objective lenses, the losses from the condenser should
be purely transmission losses, allowing you to accurately back-calculate
the intensity at the sample plane.  Obviously, make sure the aperture stop
is wide open.

Cheers,
   Ben Smith



On Fri, Mar 15, 2019 at 12:14 PM Jim Haley <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Are you trying to measure relative light output at the various
> proximities or absolute light output in terms of units such as Lux?
>
> Thanks And Have a Great Day!
>
> Jim Haley
>
>
>
> ******************************
>
> Jim Haley
>
> Applications Engineer
>
> MVIA, Inc.
>
> P.O. Box 161
>
> Monaca, PA 15061
>
>   voice:     [phone]
>
>   fax:       [phone]
>
>   e-mail:    [hidden email]  <mailto:[hidden email]>
>
>   MVIA Website  <http://www.mvia.com/>
>
>   Digital Microscope Cameras from MVIA  <
> http://www.mvia.com/Digcams/dig_cameras.html>
>
>   Image Analysis Software from MVIA  <
> http://www.mvia.com/IASoftware/ia_software.html>
>
> ******************************
>
>
> On 3/15/2019 11:08 AM, Claire Brown, Dr. wrote:
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Hello All,
> >
> > We are trying to measure the power of a light source through a 63x oil
> immersion lens. With the short focal distance the power we measure is
> highly dependent on the position of the sensor relative to the lens.
> >
> > Can the power be measured this way or do we need to get a sensor that we
> can put oil on and use oil immersion to really get a proper measure of the
> power at the sample?
> >
> >
> > Sincerely,
> >
> > Claire
> >
>

--
Benjamin E. Smith, Ph. D.
Imaging Specialist, Vision Science
University of California, Berkeley
195 Life Sciences Addition
Berkeley, CA  94720-3200
Tel  [phone]
Fax [phone]
e-mail: [hidden email]
http://vision.berkeley.edu/?page_id=5635 <http://vision.berkeley.edu/>

[Craig Brideau]

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*****

Those are very good points Ben! Unless you have a fancy beam diameter
controller the tendency in a multi-objective system is to set the beam size
for the largest back aperture and just accept that it will be clipped for
the smaller aperture lenses. This will cause a great deal of apparent power
loss, but as Ben points out wrecks any hope of a fair comparison between
lenses. He also nicely explained the point about not focusing on the sensor
surface that I tried to get at earlier. Thanks!

Craig

On Fri, Mar 15, 2019 at 3:57 PM Benjamin Smith <[hidden email]>
wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> A few quick notes:
> 1) Be careful comparing between objectives.  Not only is the transmission
> efficiency different, but the area of the back aperture is also different,
> meaning the amount of light going into an objective also varies.  Also,
> unless the light intensity profile at the back aperture is a perfectly
> uniform top hat, the difference in light going into an objective won't be
> as simple as the ratio of the back aperture areas.
>
> 2) With high NA objectives, you run into an additional problem of
> increasing amounts of light reflecting off of the power meter (think
> Brewster's angle).  As such, a lot of the marginal photons will reflect,
> reducing the overall measurement.
>
> 3) As already mentioned, the back reflection due to the glass-air interface
> at the objective lens will also reduce the amount of transmitted light
> compared to a glass-oil interface, and even more so if the objective lens
> is scratched or dirty.
>
> 4) Power meters can saturate and become non-linear if all the light is
> shined on it in a very small area.  Ideally, you will want to cover as much
> of the sensor as possible, especially at higher intensities.
>
> With this in mind, a quick and dirty solution would be to get the objective
> as close to (if not lightly touching) the sensor area as possible, and then
> gradually increase the light intensity until you get a stable measurement.
> Then gradually pull the objective away until you reach a peak power
> reading.  The objective may need to be able to get within a millimeter of
> the sensor to have the marginal rays stay within the sensor area.  Due to
> the issues stated above, this will be a slight underestimation, but it will
> definitely get you in the ball park.
>
> If you need a much more accurate measurement, an oil immersion compatible
> power meter seems the best (although fairly expensive) option:
> https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=2191
>
> One other option that comes to mind would be if you had an oil immersion
> condenser, you could use it to recollimate the light from the first
> objective, and then place the power meter at the back aperture of the
> condenser.  With everything lined up correctly, and without any scattering
> material between the objective lenses, the losses from the condenser should
> be purely transmission losses, allowing you to accurately back-calculate
> the intensity at the sample plane.  Obviously, make sure the aperture stop
> is wide open.
>
> Cheers,
>    Ben Smith
>
>
>
> On Fri, Mar 15, 2019 at 12:14 PM Jim Haley <[hidden email]> wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > Post images on http://www.imgur.com and include the link in your
> posting.
> > *****
> >
> > Are you trying to measure relative light output at the various
> > proximities or absolute light output in terms of units such as Lux?
> >
> > Thanks And Have a Great Day!
> >
> > Jim Haley
> >
> >
> >
> > ******************************
> >
> > Jim Haley
> >
> > Applications Engineer
> >
> > MVIA, Inc.
> >
> > P.O. Box 161
> >
> > Monaca, PA 15061
> >
> >   voice:     [phone]
> >
> >   fax:       [phone]
> >
> >   e-mail:    [hidden email]  <mailto:[hidden email]>
> >
> >   MVIA Website  <http://www.mvia.com/>
> >
> >   Digital Microscope Cameras from MVIA  <
> > http://www.mvia.com/Digcams/dig_cameras.html>
> >
> >   Image Analysis Software from MVIA  <
> > http://www.mvia.com/IASoftware/ia_software.html>
> >
> > ******************************
> >
> >
> > On 3/15/2019 11:08 AM, Claire Brown, Dr. wrote:
> > > *****
> > > To join, leave or search the confocal microscopy listserv, go to:
> > > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > > Post images on http://www.imgur.com and include the link in your
> > posting.
> > > *****
> > >
> > > Hello All,
> > >
> > > We are trying to measure the power of a light source through a 63x oil
> > immersion lens. With the short focal distance the power we measure is
> > highly dependent on the position of the sensor relative to the lens.
> > >
> > > Can the power be measured this way or do we need to get a sensor that
> we
> > can put oil on and use oil immersion to really get a proper measure of
> the
> > power at the sample?
> > >
> > >
> > > Sincerely,
> > >
> > > Claire
> > >
> >
>
>
> --
> Benjamin E. Smith, Ph. D.
> Imaging Specialist, Vision Science
> University of California, Berkeley
> 195 Life Sciences Addition
> Berkeley, CA  94720-3200
> Tel  [phone]
> Fax [phone]
> e-mail: [hidden email]
> http://vision.berkeley.edu/?page_id=5635 <http://vision.berkeley.edu/>
>